This invention relates to an accumulator charging valve having a pressure port connected to a source of pressure-transmitting fluid, a first user port connectible with a first user component, a second user port connectible with a pressure accumulator and a second closed-center user component, and a valve device operative in response to the accumulator pressure through which the pressure port is connectible with the second user port via a throttle below a specific accumulator pressure and is connectible with the first user port above a specific accumulator pressure. The valve device includes a non-return valve controllable by a control pressure and adapted to shut off the connection of the pressure port to the first user port below the specific accumulator pressure.
An accumulator charging valve of the aforementioned type is known from German Pat. DE-OS No. 2,364,413. In this accumulator charging valve, with the accumulator loaded, the fluid delivered by the source of pressure-transmitting fluid is completely fed through the open non-return valve to the first user component which may be a power steering gear operating according to the open-center principle.
If the accumulator pressure drops below a predetermined level, the valve device will switch such that the passageway of the non-return valve is at least largely closed and the fluid delivered is supplied to the pressure accumulator until it is again pressurized to its predetermined level. The accumulator pressure will, however, drop not only when the second user component, which may be a brake booster in an automotive vehicle, for example, is added to the circuit, but also as a result of leakage in the individual valves. If the second user component is rarely activated, which is the case, for example, when travelling long distances on a roadway where the brake is rarely applied, the pressure accumulator will become depleted after some time by leakage. In that case, whenever the accumulator pressure drops below a predetermined magnitude, the pump forming the source of pressure-transmitting fluid, which, with the accumulator loaded, delivers fluid to the reservoir at low pressure through the non-return valve and the power steering gear which is usually operated in the open-center mode, is required to recharge the accumulator at a high pressure although there is presently no fluid demand at the second user component, i.e., the brake booster.
However, when fluid is delivered at a high pressure, the pump noise will increase substantially as compared to the delivery of fluid at low pressure. Such noise is very annoying, in particular when the accumulator charging valve is fitted to an automotive vehicle.